1. Field of the Invention
Various embodiments of the present invention generally relate to producing formation fluid from a reservoir, and more particularly, to controlling the flow of fluids between the reservoir and the annulus region.
2. Description of the Related Art
A completion string may be positioned in a well to produce fluids from one or more formation zones. Completion devices may include casing, tubing, packers, valves, pumps, sand control equipment and other equipment to control the production of hydrocarbons. During production, fluid flows from a reservoir through perforations and casing openings into the wellbore and up a production tubing to the surface. The reservoir may be at a sufficiently high pressure such that natural flow may occur despite the presence of opposing pressure from the fluid column present in the production tubing. However, over the life of a reservoir, pressure declines may be experienced as the reservoir becomes depleted. When the pressure of the reservoir is insufficient for natural flow, artificial lift systems may be used to enhance production. Various artificial lift mechanisms may include pumps, gas lift mechanisms, and other mechanisms. One type of pump is the electrical submersible pump (ESP).
An ESP normally has a centrifugal pump with a large number of stages of impellers and diffusers. The pump is driven by a downhole motor, which is typically a large three-phase AC motor. A seal section separates the motor from the pump for equalizing internal pressure of lubricant within the motor to that of the well bore. Often, additional components may be included, such as a gas separator, a sand separator and a pressure and temperature measuring module. Large ESP assemblies may exceed 100 feet in length.
An ESP is typically installed by securing it to a string of production tubing and lowering the ESP assembly into the well. The string of production tubing may be made up of sections of pipe, each being about 30 feet in length.
If the ESP fails, the ESP may need to be removed from the wellbore for repair at the surface. Such repair may take an extended amount of time, e.g., days or weeks. When the ESP is removed from the wellbore, some action is typically taken to ensure that formation fluid does not continue to flow to the surface. This is typically done, for example, by applying some type of heavy weight fluid (also commonly referred to as “kill fluid”) into the wellbore to “kill” the well, i.e., to prevent fluid flow from the reservoir to the surface during work-over operations. The hydrostatic pressure from the kill fluid is typically greater than the reservoir pressure. However, when the reservoir pressure exceeds the hydrostatic pressure, fluid from the reservoir often flows to the surface during work-over operations. In some instances, the “kill” fluid might damage the reservoir making it harder to recover the oil later.
Therefore, a need exists in the art for an improved apparatus and system for controlling the flow of fluid between the reservoir and the surface.